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https://github.com/bjornbytes/trickle

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https://github.com/bjornbytes/trickle

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README 

        
Trickle

===



> **NOTE** - It's probably better to use Lua's built-in `string.pack` and `string.unpack` now.



Trickle is a bitstream for Lua.  When writing data to a trickle stream, you must specify its size in

bits.  The stream will automatically pack this data into compressed bytes, which often leads to

greatly reduced network bandwidth.  This is useful in networking applications where it is necessary

to reduce network traffic, such as realtime multiplayer games.



Usage

---



```lua

local trickle = require 'trickle'

local stream = trickle.create()



stream:write(7, '3bits')

stream:write(true, 'bool')

stream:write(1.8, 'float')



-- send over the network

-- to convert a stream to a string, call tostring(stream)

-- to convert a string to a stream, call trickle.create(string)



stream:read('3bits') -- 7

stream:read('bool') -- true

stream:read('float') -- 1.8

```



Signatures

---



A signature describes a high level template for a message.  It can be used to reduce duplication in

reading and writing of messages, and allows reading and writing of tables of data without having to

write each individual field in a specific order.  First, define a signature:



```lua

local signature = {

  { 'playerId', '4bits' },

  { 'x', '8bits' },

  { 'y', '8bits' },

  { 'direction', '9bits' } -- direction in degrees

}

```



Then, pack a message into a trickle stream using the signature:



```lua

local playerData = {

  playerId = 1,

  x = 63,

  y = 41,

  direction = 270

}



stream:pack(playerData, signature)

```



`unpack` may be used to decode the stream:



```lua

local playerData = stream:unpack(signature)

```



### Delta Groups



Let's say we only want to send the position of the player if it has changed.  Right now this isn't

possible with our signature, because we *have* to send 8 bits for the x position and 8 bits for the y

position to keep the structure of the signature uniform for the receiving end.  **Delta groups**

provide a mechanism to specify these optional groups of data.



To declare a delta group, specify a `delta` key in the signature table:



```lua

local signature = {

  { 'playerId', '4bits'},

  { 'x', '8bits' },

  { 'y', '8bits' },

  { 'direction', '9bits' },

  delta = {

    { 'x', 'y' },

    'direction'

  }

}

```



What we've done is defined two optional pieces of our message: a group for the position of the

player and a group for the direction of the player.  Now, if we pack a message like this:



```lua

local playerData = {

  playerId = 1,

  x = nil,

  y = nil,

  direction = nil

}



stream:pack(playerData, signature)

```



trickle will only pack the 4 bit player id into the message, which saves 25 bits!  Internally,

a single bit is added to the beginning of the message for each delta group, signifying whether or

not its data is present.  This means that if a delta group contains more than one key (such as the

'x' and 'y' group above), either all of the data must be present or all of it must be `nil`.  This,

for example, would result in an error:



```lua

local playerData = {

  playerId = 1,

  x = 17,

  y = nil,

  direction = 90

}



stream:pack(playerData, signature) -- Error: Only part of message delta group "x, y" was provided.

```



Documentation

---



- `trickle.create([str])` - Creates a stream.  If `str` is provided then the contents of the stream

  are set to this initial value.

- `tostring(stream)` - Serialize the stream's data to a string.

- `stream:clear()` - Resets the stream to contain no data.

- `stream:truncate()` - If a byte has been partially written, it will not be present in the stream

  yet.  `truncate` pads the rest of the byte with null data and adds it to the stream's data.  This

  is mostly for internal use, and is automatically called when converting the stream to a string.



#### Writing



- `stream:write(value, type)` - Writes a value to the stream.  `type` can either be `string`,

`float`, `bool`, or `bits` for integers, where `n` is the number of bits the integer should use.

- `stream:writeString(str)` - Writes a string to the stream.  Uses one byte per character.

- `stream:writeBool(bool)` - Writes a boolean to the stream.  Uses one bit.

- `stream:writeFloat(float)` - Writes a float to the stream.  Note that the float is currently

  serialized as a string.  This is suboptimal and should be improved in the future.

- `stream:writeBits(value, n)` - Writes a number to the stream, using `n` bits.



#### Reading



- `stream:read(type)` - Reads and returns a value from the stream.

- `stream:readString()` - Reads and returns a string.

- `stream:readBool()` - Reads and returns a boolean.

- `stream:readFloat()` - Reads and returns a float.

- `stream:readBits(n)` - Readss `n` bits from the string and returns them as a number.



#### Signatures



- `stream:pack(data, signature)` - Packs `data` into the stream according to the structure specified

  by `signature`.

- `stream:unpack(signature)` - Uses `signature` to read data from the string, returning a table with

  the data.



License

---



MIT, see [`LICENSE`](LICENSE) for details.